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排序方式: 共有239条查询结果,搜索用时 281 毫秒
1.
Aluminum based metal matrix composites are offering o utstanding properties in a number of automotive and aircraft components and body structures. The major advantages of these composite materials are their high st rength to weight ratio, high stiffness, high hardness, wear resistance, low coef ficient of thermal expansion, superior dimensional stability and versatility to designer. In addition to these their isotropic properties, good forming characte ristics, easy availability of cheaper reinforcements... 相似文献
2.
Summary The level of the acid hydrolases -glucuronidase (EC 3.2.3.11), acid phosphatase (EC 3.1.3.2) and acid protease (EC 3.4.4) was studied during larval growth and molting inP. ricini. The level of activity of these enzymes remained low during larval growth; however, the level increased sharply at the time of molting and declined sharply thereafter in the newly ecdysed insect. Interestingly, the diminished activity of these enzymes was almost quantitatively recovered in the cast-off cuticle. The excretion of acid hydrolases through the cast-off cuticle has hitherto not been reported in insects during molting. 相似文献
3.
Molasses was used as an alternative binder to the bentonite binder. The change in moisture absorption by pellets prepared with different iron ores and different molasses contents were investigated. Iron ore properties exerted the major effect on pellet behavior and final pellet quality. The absorbed moisture content of pellets prepared without binder, bentonite-added pellets, and molasses-added pellets were in the range of 7.72%–9.95%, 9.62%–10.84%, and 6.14%-6.69%, respectively. The wet pellet compressive strength of molasses-added pellets(43–230 N/pellet) was superior to that of bentonite-added pellets(9.47–11.92 N/pellet). The compressive strength of dried molasses-modified pellets increased to 222–394 N/pellet, which is currently the highest value achieved for dried pellets. 相似文献
4.
Gandhi DD Lane M Zhou Y Singh AP Nayak S Tisch U Eizenberg M Ramanath G 《Nature》2007,447(7142):299-302
Self-assembled molecular nanolayers (MNLs) composed of short organic chains and terminated with desired functional groups are attractive for modifying surface properties for a variety of applications. For example, organosilane MNLs are used as lubricants, in nanolithography, for corrosion protection and in the crystallization of biominerals. Recent work has explored uses of MNLs at thin-film interfaces, both as active components in molecular devices, and as passive layers, inhibiting interfacial diffusion, promoting adhesion and toughening brittle nanoporous structures. The relatively low stability of MNLs on surfaces at temperatures above 350-400 degrees C (refs 12, 13), as a result of desorption or degradation, limits the use of surface MNLs in high-temperature applications. Here we harness MNLs at thin-film interfaces at temperatures higher than the MNL desorption temperature to fortify copper-dielectric interfaces relevant to wiring in micro- and nano-electronic devices. Annealing Cu/MNL/SiO2 structures at 400-700 degrees C results in interfaces that are five times tougher than pristine Cu/SiO2 structures, yielding values exceeding approximately 20 J m(-2). Previously, similarly high toughness values have only been obtained using micrometre-thick interfacial layers. Electron spectroscopy of fracture surfaces and density functional theory modelling of molecular stretching and fracture show that toughening arises from thermally activated interfacial siloxane bridging that enables the MNL to be strongly linked to both the adjacent layers at the interface, and suppresses MNL desorption. We anticipate that our findings will open up opportunities for molecular-level tailoring of a variety of interfacial properties, at processing temperatures higher than previously envisaged, for applications where microlayers are not a viable option-such as in nanodevices or in thermally resistant molecular-inorganic hybrid devices. 相似文献
5.
Manipulation of host-cell pathways by bacterial pathogens 总被引:3,自引:0,他引:3
Bacterial pathogens operate by attacking crucial intracellular pathways in their hosts. These pathogens usually target more than one intracellular pathway and often interact at several points in each of these pathways to commandeer them fully. Although different bacterial pathogens tend to exploit similar pathway components in the host, the way in which they 'hijack' host cells usually differs. Knowledge of how pathogens target distinct cytoskeletal components and immune-cell signalling pathways is rapidly advancing, together with the understanding of bacterial virulence at a molecular level. Studying how these bacterial pathogens subvert host-cell pathways is central to understanding infectious disease. 相似文献
6.
Resonantly enhanced light transmission through periodic subwavelength aperture arrays perforated in metallic films has generated significant interest because of potential applications in near-field microscopy, photolithography, displays, and thermal emission. The enhanced transmission was originally explained by a mechanism where surface plasmon polaritons (collective electronic excitations in the metal surface) mediate light transmission through the grating. In this picture, structural periodicity is perceived to be crucial in forming the transmission resonances. Here we demonstrate experimentally that, in contrast to the conventional view, sharp transmission resonances can be obtained from aperiodic aperture arrays. Terahertz transmission resonances are observed from several arrays in metallic films that exhibit unusual local n-fold rotational symmetries, where n = 10, 12, 18, 40 and 120. This is accomplished by using quasicrystals with long-range order, as well as a new type of 'quasicrystal approximates' in which the long-range order is somewhat relaxed. We find that strong transmission resonances also form in these aperiodic structures, at frequencies that closely match the discrete Fourier transform vectors in the aperture array structure factor. The shape of these resonances arises from Fano interference of the discrete resonances and the non-resonant transmission band continuum related to the individual holes. Our approach expands potential design parameters for aperture arrays that are aperiodic but contain discrete Fourier transform vectors, and opens new avenues for optoelectronic devices. 相似文献
7.
8.
A genome-wide association study for celiac disease identifies risk variants in the region harboring IL2 and IL21 总被引:14,自引:0,他引:14
van Heel DA Franke L Hunt KA Gwilliam R Zhernakova A Inouye M Wapenaar MC Barnardo MC Bethel G Holmes GK Feighery C Jewell D Kelleher D Kumar P Travis S Walters JR Sanders DS Howdle P Swift J Playford RJ McLaren WM Mearin ML Mulder CJ McManus R McGinnis R Cardon LR Deloukas P Wijmenga C 《Nature genetics》2007,39(7):827-829
We tested 310,605 SNPs for association in 778 individuals with celiac disease and 1,422 controls. Outside the HLA region, the most significant finding (rs13119723; P = 2.0 x 10(-7)) was in the KIAA1109-TENR-IL2-IL21 linkage disequilibrium block. We independently confirmed association in two further collections (strongest association at rs6822844, 24 kb 5' of IL21; meta-analysis P = 1.3 x 10(-14), odds ratio = 0.63), suggesting that genetic variation in this region predisposes to celiac disease. 相似文献
9.
Community structure is an integral characteristic of real world networks whichever processes or areas they emerge from. This paper addresses the problem of community structure detection theoretically as well as computationally. The authors introduce a number of concepts such as the neighbourhood and strength of a subgraph, p-community, local maximal p-community, hubs, and outliers that play elemental role in formalising the concept of community structure in complex networks. A few preliminary results have been derived that lead to the development of an algorithm for community structure detection in undirected unweighted networks. The algorithm is based on a local seed expansion strategy that uses the concept of interaction coefficient. The authors have analysed the algorithm on a number of parameters such as accuracy, stability, and quality on synthetic and real world networks from different areas. 相似文献
10.
Anderson BH Kasher PR Mayer J Szynkiewicz M Jenkinson EM Bhaskar SS Urquhart JE Daly SB Dickerson JE O'Sullivan J Leibundgut EO Muter J Abdel-Salem GM Babul-Hirji R Baxter P Berger A Bonafé L Brunstom-Hernandez JE Buckard JA Chitayat D Chong WK Cordelli DM Ferreira P Fluss J Forrest EH Franzoni E Garone C Hammans SR Houge G Hughes I Jacquemont S Jeannet PY Jefferson RJ Kumar R Kutschke G Lundberg S Lourenço CM Mehta R Naidu S Nischal KK Nunes L Ounap K Philippart M Prabhakar P Risen SR 《Nature genetics》2012,44(3):338-342
Coats plus is a highly pleiotropic disorder particularly affecting the eye, brain, bone and gastrointestinal tract. Here, we show that Coats plus results from mutations in CTC1, encoding conserved telomere maintenance component 1, a member of the mammalian homolog of the yeast heterotrimeric CST telomeric capping complex. Consistent with the observation of shortened telomeres in an Arabidopsis CTC1 mutant and the phenotypic overlap of Coats plus with the telomeric maintenance disorders comprising dyskeratosis congenita, we observed shortened telomeres in three individuals with Coats plus and an increase in spontaneous γH2AX-positive cells in cell lines derived from two affected individuals. CTC1 is also a subunit of the α-accessory factor (AAF) complex, stimulating the activity of DNA polymerase-α primase, the only enzyme known to initiate DNA replication in eukaryotic cells. Thus, CTC1 may have a function in DNA metabolism that is necessary for but not specific to telomeric integrity. 相似文献